200ci How are these spark plugs and compression looking?

[gserafini]

Finally got to a compression test on the car to see how it's looking. Numbers don't seem too bad from what I can see, wondering what others here think? And how do these plugs look? They are very new, put in about 3 months ago and driven about 150 miles. The #5 was so tightly cranked on there that the porcelain broke when taking it out. I don't believe any got in the engine as it was all caught in the socket with the plug. The plugs were also VERY hot (warmed up the car for 5 mins). I checked the gap and they were more like .025-.030 instead of the stock .035.

 

[PSIG]

A bit oily, and obviously rich from startup choke. Inconclusive. Reading plugs shows mostly that last run-time, so all you can verify is that your warmup choke is a bit rich. Not useful for condition or tuning info except warmup in this case. Pull the plugs after a fully-warmed clean cruise shutdown, or to end a wide-open run (or whatever operating range you're checking) to see that info clearly. Easiest and clearest reading is to shut-down from that condition, including WOT.

Is #3 140 or 160? If 140 it's sick. If 160 it's the weakest and shows most deposits, but again, warmup and first start which can be sootier and oilier. The test was warm and dry, yes? Did you try adding a squirt of oil for a warm wet sealing test? If not, I'd just move to a leak-down test to confirm where the cylinders are starting to show weakness (valves, rings, etc) so you have an idea what to expect is coming. IMO, numbers appear OK for a grocery getter/cruiser. Vacuum tests can also help create a bigger picture. Have fun!

 

[gserafini]

A bit oily, and obviously rich from startup choke. Inconclusive. Reading plugs shows mostly that last run-time, so all you can verify is that your warmup choke is a bit rich. Not useful for condition or tuning info except warmup in this case. Pull the plugs after a fully-warmed clean cruise shutdown, or to end a wide-open run (or whatever operating range you're checking) to see that info clearly. Easiest and clearest reading is to shut-down from that condition, including WOT.

Is #3 140 or 160? If 140 it's sick. If 160 it's the weakest and shows most deposits, but again, warmup and first start which can be sootier and oilier. The test was warm and dry, yes? Did you try adding a squirt of oil for a warm wet sealing test? If not, I'd just move to a leak-down test to confirm where the cylinders are starting to show weakness (valves, rings, etc) so you have an idea what to expect is coming. IMO, numbers appear OK for a grocery getter/cruiser. Vacuum tests can also help create a bigger picture. Have fun!

Thanks for the info/input! Yes that #3 was 140 and checked it twice. I did not put any oil down. Just warmed up the car so choke was open, then tied the choke open, pulled the plugs and and coil wire. Then cranked for each cylinder with foot down on the throttle. Also did a vacuum test with it warm and running, and was getting about 17. Though it was bouncing a bit between 16-18 wouldn't really hold exactly steady

 

[PSIG]

Though it was bouncing a bit between 16-18 wouldn't really hold exactly steady

Signs of a bigger picture. Leak-down is next, then decide the future from there on your terms.

 

[gserafini]

Signs of a bigger picture. Leak-down is next, then decide the future from there on your terms.

Yes...i'm trying to learn what all the signs mean haha

 

[PSIG]

More data (info and sources) greatly improves and reinforces crystal ball vision.

 

[aussie7mains]

For an everyday hack, its fine, just drive it. If your looking at ideals, then the valves need further assesment, a leakdown test will tell you what is going of. Idealy compression pressure should be fairly even, +- 10psi and 170psi is a good number for Falcon six. Plugs look a bit sooty, but as stated above, not actually very meaningfull.

 

[gserafini]

For an everyday hack, its fine, just drive it. If your looking at ideals, then the valves need further assesment, a leakdown test will tell you what is going of. Idealy compression pressure should be fairly even, +- 10psi and 170psi is a good number for Falcon six. Plugs look a bit sooty, but as stated above, not actually very meaningfull.

Thanks! I will drive it like I stole it while I make more plans for the future. Also sorry I forgot to say in this threat it’s a 66 mustang 200.
Yes leak down next, do you guys have tips on how to do it right?? I’ll also read the manual on it but still asking. And hoping I can rent a gauge for it from the auto store

 

[PSIG]

You're just judging health by how much air leaks out of a sealed cylinder (top-center, valves closed). One part of the test is reading leak-down, and the other is determining where the leak(s) are. I do leak-down at 100 psi, as that makes all readings direct percent leakage, e.g., 93 psi is 7% leak-down.

I use a home-made tool (below), and set pressure with my thumb over the open end, adjusting the compressor regulator until the leak-down gauge reads 100. I install in the cylinder that is at TDC compression stroke. I mark the damper in quarters (V8) or thirds (I6) so I'm sure it's right at TDC, or the air pressure will spin the crank around. That sucks if your wrench is still on the crank bolt. Turn the air on and read the gauge.

Leakdown is judgmental for the type of build. A blueprinted and carefully-broken-in racing engine may have 1 to 3% leak-down. Performance engines in good shape 5 to 10%. Mom's car 10-20%. Beyond that is on it's way out the door, and while 30% might still limp to the grocery, it's on last legs and suffering badly. So for me, if it's towards the high-end for the type, I'll find what's leaking by sound.

Hissing heard at the oil filler cap are rings. From the carb is intake valve, and from the exhaust is exhaust valve. Stuff like that. A tired engine will be hissing everywhere. Turn the crank 90° for the next cylinder in firing order. Test at part-stroke or BDC for comparative readings, such as 18% at TDC and 7% at BDC is a worn tapered bore. Bubbling in the radiator at TDC is probably a gasket, or at BDC is likely a crack. More on making and using one by Mike Nixon 25+ years ago here: https://www.wheelhorseforum.com/topic/8183-leak-down-tester/

Here' is the DIY build in the article, bigger so you can see it. Note only one gauge is needed, as it is after the damper (restrictor), and pressure set closed-off. I simplified mine by using a Tee with 2 male ends and no regulator, using the one on the compressor. Leakdown testers are under $30 online these days if you're not the DIY type, and many auto parts stores loan them for free:

 

[gserafini]

You're just judging health by how much air leaks out of a sealed cylinder (top-center, valves closed). One part of the test is reading leak-down, and the other is determining where the leak(s) are. I do leak-down at 100 psi, as that makes all readings direct percent leakage, e.g., 93 psi is 7% leak-down.

I use a home-made tool (below), and set pressure with my thumb over the open end, adjusting the compressor regulator until the leak-down gauge reads 100. I install in the cylinder that is at TDC compression stroke. I mark the damper in quarters so I'm sure it's right at TDC, or the air pressure will spin the crank around. That sucks if your wrench is still on the crank bolt. Turn the air on and read the gauge.

Leakdown is judgmental for the type of build. A blueprinted and carefully-broken-in racing engine may have 1 to 3% leak-down. Performance engines in good shape 5 to 10%. Mom's car 10-20%. Beyond that is on it's way out the door, and while 30% might still limp to the grocery, it's on last legs and suffering badly. So for me, if it's towards the high-end for the type, I'll find what's leaking by sound.

Hissing heard at the oil filler cap are rings. From the carb is intake valve, and from the exhaust is exhaust valve. Stuff like that. A tired engine will be hissing everywhere. Turn the crank 90° for the next cylinder in firing order. Test at part-stroke or BDC for comparative readings, such as 18% at TDC and 7% at BDC is a worn tapered bore. Bubbling in the radiator at TDC is probably a gasket, or at BDC is likely a crack. More on making and using one by Mike Nixon 25+ years ago here: https://www.wheelhorseforum.com/topic/8183-leak-down-tester/

Here' is the DIY build in the article, bigger so you can see it. Note only one gauge is needed, as it is after the damper (restrictor), and pressure set closed-off. I simplified mine by using a Tee with 2 male ends and no regulator, using the one on the compressor. Leakdown testers are under $30 online these days if you're not the DIY type, and many auto parts stores loan them for free:
View attachment 21415

Wow thank you for all the tips! That's super useful thank you. I shall expect some hissing all over and hope for around 25-30% haha!

 

[PSIG]

Hard to say, and why we do testing like this. Information rules. If you find little loss past the rings, but a lot from your valves, then you know you could option doing just a head job and get back on the road for minimal but effective expense. Put your effort and money where the problems are. Data and good judgment can greatly extend the lifespan and performance of the engine at minimum costs.